Avoid replaying already-posted daily notifications

[kentoku24]

Summary

• treat a pending Discord daily notification as delivered if the exact message is already visible from the bot in the target channel
• avoid replaying the same pending daily notification every scheduled run after an ambiguous delivery failure
• cover the recovery path with a runner test and extend the fake Discord client with read helpers

Context

• observed duplicate daily notifications on March 26, 2026 JST after earlier runs reported delivery failure: 1件
• the repeated hourly posts are consistent with a pending daily message being replayed on every scheduled run

Verification

• /Users/kentokumatsunami/Documents/GitHub/comic_crawler/.venv/bin/python -m unittest tests.test_runner tests.test_discord_outbound
• /Users/kentokumatsunami/Documents/GitHub/comic_crawler/.venv/bin/python -m unittest discover -s tests -p 'test_*.py'
• git diff --check

Residual Risks

• this fixes the "message actually appeared but delivery was treated as failed" replay case by checking recent channel history; it does not change genuine repeated failures where Discord never accepted the message

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Scan more than 10 messages before suppressing a retry

The replay suppression check only inspects the latest 10 channel messages, so if more than 10 messages are posted after an ambiguous failure, the previously delivered daily notification is missed and the pending item is re-sent again on the next run. In active channels this recreates the duplicate-post loop this change is trying to prevent; consider paginating history (or scanning since created_at) instead of hard-capping at 10.

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